In a generating machining method, the rotational movements of the tool and of the workpiece are coupled such that the gear teeth of the tool roll off on the gear teeth of the workpiece, the so-called generating coupling. The generating movement thus corresponds to that of a gear train formed by the tool and the workpiece. The generating movement is a relative movement between the tool and the workpiece in the direction of the workpiece width, i.e. superposed in the direction of the axis of rotation of the workpiece, by which the tool is guided along the workpiece in a machining stroke.
The center distance between the workpiece and the tool defines the engagement depth of the tool into the workpiece and permits an influencing of the tooth thickness. The axial cross angle in known generating machining methods is predefined by the helix angle of the tool and of the workpiece.
A desired tooth trace shape and/or tooth thickness of the gear teeth can be generated by such a generating machining method. The term tooth trace shape on the one hand comprises an unmodified tooth trace in the sense of the invention. The term tooth trace shape on the other hand comprises a tooth trace modification in the sense of the invention.
It is already known from the prior art to predefine a modified tooth trace and to generate it by a generating machining method. It is known for this purpose from DE 102 085 31 to generate a free tooth trace modification on the left and right tooth flanks of the workpiece by a variation of the center distance in dependence on the workpiece width position and on a corresponding correction of the generating coupling.
It is the object of the present invention to extend the possibilities of generating machining.
This object is achieved by a process in accordance with claim 1. Advantageous embodiments of the present invention form the subject of the dependent claims.
The present invention comprises a process for gear manufacturing machining of a workpiece by a tool on a gear manufacturing machine, wherein the workpiece is machined by a generating machining method in which the tool for the gear manufacturing machining rolls off on the workpiece at a predefined center distance and axial cross angle. A desired tooth trace shape and/or tooth thickness of the gear teeth is generated by the generating machining method. In accordance with the invention, an additional condition can be predefined, wherein the center distance and the axial cross angle are determined in dependence on the desired tooth trace shape and/or on the tooth thickness of the gear teeth and on the additional condition.
The inventor of the present invention has recognized that a further degree of freedom of gear manufacturing machining becomes available via the axial cross angle and said degree of freedom can be used to extend the possibilities of generating machining. This further degree of freedom permits an additional condition to be predefined in the generating machining in dependence on which the center distance and the axial cross angle are determined.
The process in accordance with the invention is preferably used in two-flank generating machining.
The present invention can in particular be used in gear hobbing and in generating grinding. In gear hobbing, a blank is machined that still has no gear teeth, that typically has a rotationally symmetrical shape and that is only provided with gear teeth by the gear hobbing process. Gear hobbing typically takes place in a plurality of machining strokes.
In generating grinding, a blank is typically machined that already has gear teeth, wherein generating grinding is used to improve the quality of the gear teeth geometry. Generating grinding is in particular a hard fine machining. The blank that already has gear teeth is typically surface hardened prior to the carrying out of generating grinding. Generating grinding preferably takes place in a plurality of machining strokes and in particular in at least one rough machining cut and at least one finishing cut.
The workpieces preferably consist of metal, in particular steel. In gear hobbing, a hob is typically used as the tool; in generating grinding, a grinding worm is typically used. The grinding worm can be a dressable tool or a non-dressable tool.
Within the framework of the present invention, an axial cross angle is preferably used that differs from an axial cross angle that is predefined by the helix angle of the tool and of the workpiece and that was used in the prior art. The deviation of the axial cross angle from an axial cross angle predefined by the helix angles of the tool and of the workpiece is preferably selected in dependence on the additional condition. The center distance is then preferably set such that the desired tooth trace and/or tooth thickness is generated despite the deviating axial cross angle.
The inventor of the present invention has recognized that the tooth thickness can be changed by a change of the axial cross angle. The tooth thickness can in particular be reduced by a deviation from the axial cross angle predefined by the helix angles of the tool and of the workpiece. An increase in the tooth thickness that is caused by a larger center distance can therefore be compensated by a corresponding setting of the axial cross angle. This permits the center distance to be freely selected within certain limits and nevertheless to achieve the desired tooth trace shape by a corresponding selection of the axial cross angle. It is in turn possible to satisfy an additional condition by the setting of the center distance.
The center distance and the difference between the axial cross angle to be set and the axial cross angle predefined by the helix angles of the tool and of the workpiece is preferably determined in accordance with the invention in dependence on the additional condition and on the desired tooth trace shape and/or tooth thickness. The center distance can in particular be set in dependence on the additional condition and the axial cross angle can thus in particular be determined such that the desired tooth trace shape and/or tooth thickness is/are produced.
Provision can furthermore be made in accordance with the invention that a specific setting of the correction of the generating coupling takes place in addition to a specific setting of the center distance and of the axial cross angle.
A correction of the generating coupling in dependence on the workpiece width position can be achieved by a plurality of different machine axes. A correction of the generating coupling can in particular be achieved by an additional rotational movement of the workpiece and/or of the tool. The correction of the generating coupling can, however, also be achieved by a shift movement and/or, with a helical gear, by an axial feed movement of the workpiece. The movements preferably take place in dependence on the workpiece width position.
The center distance, the axial cross angle and a correction of the generating coupling can be determined in accordance with the invention in dependence on the desired tooth trace shape and/or tooth thickness and on the additional condition. The correction of the generating coupling permits an influencing of the tooth trace shape that has a different effect on the left and right tooth flanks. The tooth trace shape and/or the tooth thickness at the left and right tooth flanks can thus be predefined independently by a setting of the center distance and of a corresponding correction of the generating coupling.
In accordance with the invention, a tooth flank modification can be predefined as the desired tooth trace, with the tooth thickness and/or the tooth trace modification preferably being predefinable independently for the left and right tooth flanks.
Alternatively or additionally, the center distance and/or the correction of the generating coupling can be determined as a function of the workpiece width position. Freely predefinable tooth trace modifications can be generated on the right and left tooth flanks within certain conditions in accordance with the invention by a center distance variable in dependence on the workpiece width position and by a corresponding correction of the generating coupling. The setting of the center distance in accordance with the invention additionally permits the satisfaction of an additional condition.
The additional condition that can be predefined in accordance with the invention and that can be satisfied by setting the axial cross angle preferably relates to the geometry of the gear teeth.
In a first variant of the present invention, the additional condition can be a specification with respect to the shape of the gear teeth in the inactive part of the gear teeth. In a second variant of the present invention, the additional condition can in contrast be a specification of the shape of the gear teeth in the active part of the gear teeth. The inactive part of the gear teeth is in particular the non-involute part of the gear teeth, in particular the root and/or the tip. The active part of the gear teeth is in particular the involute part of the gear teeth, in particular the left and/or right tooth flank.
Within the framework of the first variant, the specification can relate to the root geometry, in particular to the root radius and/or to the extent of the root, and/or to the tip geometry, in particular to the tip radius and/or to the extent of the tip, of the gear teeth generated on the workpiece. A specification relating to the root geometry is particularly relevant within the framework of the present invention.
Within the framework of the second variant, in which the additional condition relates to a specification relating to the shape of the gear teeth in the active part of the gear teeth, the specification can in particular relate to the position of a modification generated on the active tooth flank of the workpiece by a modification on the tool.
The root radius or the tip radius of the gear teeth generated on the workpiece can therefore in particular be predefined as the additional condition, wherein a corresponding root radius or tip radius is generated by a corresponding setting of the axial cross angle and of the center distance within the framework of the process in accordance with the invention.
Alternatively, the position of a modification generated on the active tooth flank of the workpiece can be predefined as the additional condition, wherein a corresponding position of the modification is generated by a corresponding setting of the axial cross angle and of the center distance within the framework of the process in accordance with the invention.
If only one additional condition is predefined in accordance with the invention, this can preferably be exactly satisfied by the process in accordance with the invention. The center distance and the axial cross angle and, optionally, the correction of the generating coupling are in particular determined in accordance with the invention such that the desired tooth trace shape and/or the tooth thickness is/are generated and the additional condition is exactly satisfied.
Within the framework of the present invention, however, two or more additional conditions can also be predefined, in particular two of the above-named additional conditions. A first specification relating to the shape of the gear teeth in the inactive part of the gear teeth and a second specification relating to the shape of the gear teeth in the active part of the gear teeth can in particular be predefinable. A specification relating to the root radius and/or tip radius and a specification relating to the position of a modification generated on the active tooth flank of the workpiece by a modification on the tool can in particular be provided in accordance with the invention. In this case, the two or more additional conditions can, however, typically no longer be exactly satisfied. The center distance and the axial cross angle and, optionally, a correction of the generating coupling are therefore preferably determined by means of a curve fitting such that the two or more additional conditions are satisfied in an ideal approximation.
The present invention permits a plurality of new applications that will be explained in more detail in the following:
In a first variant, in accordance with the invention, the root can be processed together with the active tooth flank in at least one machining stroke. In accordance with the invention, the tooth thickness generated in this machining stroke and the root radius generated in this machining stroke are predefinable separately and/or the material removal in the region of the root and of the tooth flank can be set separately. In accordance with the invention, the tooth thickness generated in this machining stroke and the root radius generated in this machining stroke are generated by a suitable setting of the axial cross angle and of the center distance between the tool and the workpiece.
The inventor of the present invention has recognized that the material removal in the region of the root substantially only depends on the center distance and, in contrast, not on the axial cross angle. The material removal in the region of the tooth flanks, in contrast, depends on the center distance and on the axial cross angle. In accordance with the invention, the center distance can therefore be set in dependence on the predefined root radius or in dependence on the predefined material removal in the region of the root and the axial cross angle can be set in dependence on the center distance determined in this manner such that the desired tooth thickness or the desired material removal is achieved in the region of the tooth flanks.
The process in accordance with the invention has considerable advantages over methods known from the prior art in which the material removal was not separately settable on the tooth flanks and in the root. This could have the result that a technologically unfavorably large material removal would take place in the root or that an unnecessarily small material removal would have to be selected on the tooth flanks.
The material removal on the right and left tooth flanks is preferably separately predefinable within the framework of the present invention. A corresponding material removal is preferably generated by a suitable setting of the axial cross angle and of the center distance between the tool and the workpiece and of a suitable correction of the generating coupling. An independent setting of the material removal on the right and left tooth flanks is in turn possible by the correction of the generating coupling.
In a second variant that is preferably carried out in accordance with the first variant, the workpiece is machined with a plurality of machining strokes, wherein the root is machined together with the active tooth flank in at least one machining stroke. The setting of the axial cross angle and of the center distance between the tool and the workpiece takes place such that the material removal in the region of the root is smaller in the last machining stroke than in a preceding machining stroke. The inventor of the present invention has recognized that the amount of the material removal in the region of the root has an effect on the quality of the gear teeth in the active region of the tooth flank. If the material removal for the last machining stroke is therefore selected as small in the region of the root, the negative effects on the gear manufacturing quality in the region of the tooth flanks are reduced.
The material removal in the region of the root in all the preceding machining strokes is preferably larger than or equal to the material removal in the region of the root in the last machining stroke. Alternatively or additionally, no material removal at all can take place in the root region in the last machining stroke.
In a third variant that can optionally be combined with the first and/or second variants, the root is machined together with the active tooth flank in at least one machining stroke, while the root is not co-machined in at least one other machining stroke. This can have technological advantages, on the one hand; it increases the degrees of freedom in the machining of the active tooth flank, on the other hand.
No modification caused by a variation of the axes of movement of the gear manufacturing machine is preferably generated in the one machining stroke in which the root is machined together with the active tooth flank. This has the advantage that no modification is applied to the root. In contrast, in the other machining step, a modification of the active tooth flank caused by a variation of the axes of movement is preferably generated, while the tool remains out of engagement with the root. In accordance with the invention, a sufficiently large distance is selected between the root of the gear teeth of the workpiece and the tip of the tool in accordance with the invention such that, despite the variation of the axes of movement by which the modification of the active tooth flank is generated, the tool remains out of engagement with the root of the gear teeth generated on the workpiece.
The variation of the axes of movement by which the modification of the active tooth flank is generated can in particular be a variation of the center distance and/or of the axial cross angle and/or of the correction of the generating coupling. The center distance and/or the axial cross angle and/or a correction of the generating coupling are preferably therefore changed in the other machining stroke for producing a tooth trace modification of the active tooth flank in dependence on the workpiece width position.
The present invention permits the use of a combination dressing tool in generating grinding for the dressing of the grinding worm used as the tool, wherein the combination dressing tool simultaneously dresses at least one left and one right tooth flank and one tip of the grinding worm. The tooth thickness and the tip radius of the grinding worm are admittedly hereby dependent on one another. In accordance with the invention, a desired root radius and a desired tooth trace shape and/or tooth thickness of the gear teeth to be generated on the workpiece can nevertheless be generated by a suitable setting of the center distance and of the axial cross angle and, optionally, by a suitable correction of the generating coupling between the tool and the workpiece in the machining of the workpiece.
A combination dressing tool in the sense of the present invention can in particular be a dressing roller and/or a combination of dressing rollers and/or a multi-ribbed dressing roller and/or a dressing gear wheel.
In the above-described variants of the present invention, the additional condition respectively referred to a specification relating to the geometry of the gear teeth to be generated in the region of the root and/or of the tip, in particular to a specification of a desired root radius. The present invention is, however, not restricted to such additional conditions that relate to the inactive region of the gear teeth.
In a further variant of the present invention, a tool is used that has a modification that is applied to the active tooth flank of the workpiece during gear manufacturing machining. The position of the modification on the active tooth flank of the workpiece is predefinable and/or variable in accordance with the invention and/or is set via the setting of the axial cross angle and of the center distance between the tool and the workpiece.
The inventor of the present invention has recognized that the position of the modification on the active tooth flank of the workpiece depends in different manners on the center distance and on the axial cross angle. The position of the modification depends more on the center distance, but also less on the axial cross angle. The center distance can therefore be set in a first approximation in dependence on the desired position of the modification on the active tooth flank of the workpiece, wherein the axial cross angle is then set in dependence on this center distance such that the desired tooth thickness and/or tooth trace shape is generated. However, an equation system in the parameters center distance and axial cross angle and, optionally, correction of the generating coupling has to be solved for the exact determination of the center distance and of the axial cross angle so that both the desired position of the modification and the tooth thickness and/or tooth trace shape are achieved.
A possible application comprises a tool being used whose modification was configured for a different desired workpiece geometry, wherein the position of the modification on the workpiece is adapted to the new desired workpiece geometry via the setting of the axial cross angle and of the center distance between the tool and the workpiece. For example, a tool can thus be used that is actually configured for the desired workpiece geometry of a gear wheel that forms a gear train pair with the gear wheel to be machined.
The modification of the tool used in accordance with the invention can in particular be generated by a corresponding modification of the dressing tool. The tool can in particular be dressed within the framework of the present invention using a dressing tool that has a profile modification that is transferred to the tool by the dressing. A dressing tool can in particular be used that simultaneously dresses at least one left tooth flank and one right tooth flank. A dressing roller and/or a combination of dressing rollers and/or a multi-ribbed dressing roller and/or a dressing gear wheel can in particular be used as the dressing tool.
If the left and right tooth flanks are dressed simultaneously, the position of the profile modification during dressing can no longer be set independently of the tooth space width or tooth thickness of the gear teeth of the tool.
The present invention, however, permits the position of the modification on the workpiece to be adapted to the desired workpiece geometry via the setting of the axial cross angle and of the center distance between the tool and the workpiece and in particular to generate the position of the modification as desired and nevertheless also to generate the desired tooth thickness and/or tooth trace shape.
Work can be carried out within the framework of the present invention with an axial cross angle constant over the workpiece width in at least one machining stroke. Work can furthermore also be carried out with an axial cross angle constant over the workpiece width in all the machining strokes. A constant axial cross angle can in particular be determined within the framework of the invention for a respective machining stroke in dependence on the additional condition and can be used in gear manufacturing machining. It is, however, also possible within the framework of the present invention to vary the axial cross angle in dependence on the workpiece width.
In a further independent aspect, the present invention comprises a gear manufacturing machine having a tool holder and a workpiece holder as well as NC axes for setting the relative position between the tool and the workpiece for gear manufacturing machining a workpiece held in the workpiece holder by a tool held in the tool holder. The gear manufacturing machine comprises a control for controlling the NC axes for carrying out a generating machining method in which the tool for the gear manufacturing machining rolls off on the workpiece. The control has an input function by which a desired tooth trace shape and/or tooth thickness and an additional condition are predefinable. The control furthermore has a machining function that sets the center distance and the axial cross angle between the workpiece and the tool during generating machining such that the machined workpiece has the desired tooth trace shape and/or tooth thickness and satisfies the additional condition.
As already described above, the desired tooth trace shape can be both an unmodified tooth trace and a tooth trace modification. The present invention thus also relates to such a gear manufacturing machines whose input function does not permit any predefinition of a tooth trace modification. However, the present invention preferably relates to gear manufacturing machines in which a tooth trace modification is predefinable via the input function.
Alternatively or additionally, a tooth thickness generated in a machining stroke and/or a root radius generated in a machining stroke can be separately predefinable by the input function. Further alternatively or additionally, the material removal can be separately predefinable on the right and left flanks and in the root. The machining function preferably correspondingly controls the center distance, the axial cross angle and, optionally, a correction of the generating coupling to generate the tooth thickness and/or the root radius or to carry out the predefined material removal.
The control of the NC axes by the machining function preferably takes place in an automated manner in dependence on the predefined tooth trace shape and/or tooth thickness and on the additional condition.
The additional condition can in particular be an additional condition such as was described above. The input function and the machining function are further preferably designed such that one of the above-described processes can be carried out via the gear manufacturing machine in accordance with the invention. The machining function is preferably configured such that it carries out a generating machining in accordance with one of the processes presented above in an automated manner in dependence on the inputs and/or specifications.
In a further independent aspect, the present invention comprises a calculation apparatus for calculating the relative positions between the tool and the workpiece required for the carrying out of generating machining. Such a calculation apparatus can in particular comprise a microprocessor and a memory with software being stored in the memory that runs in the microprocessor. The present invention furthermore comprises software for calculating the relative position between the tool and the workpiece required for carrying out generating machining.
The calculation apparatus and/or software comprises an input function by which a desired tooth trace shape and/or tooth thickness and an additional condition are predefinable as well as a determination function that determines the center distance and the axial cross angle between the workpiece and the tool during generating machining such that the machined workpiece has the predefined tooth trace shape and/or tooth thickness and satisfies the additional condition. The determination function furthermore preferably determines a correction of the generating coupling during generating machining.
The input function and the determination function are preferably configured such that a calculation of the relative position between the tool and the workpiece required for carrying out a process in accordance with the invention such as was described above is possible via the determination function. The input function is furthermore preferably configured such that the specifications presented above, and in particular at least one of the additional conditions presented above, are predefinable.
The calculation apparatus and/or the software can be part of a gear manufacturing machine in accordance with the invention, wherein the data determined by the determination function are used by the machining function for machining a workpiece.
Alternatively, the calculation apparatus and/or the software can be an apparatus separate from a gear manufacturing machine. The calculation apparatus and the software, however, preferably have an interface by which the data determined by the determination function can be transmitted to a gear manufacturing machine such that it can carry out generating machining on the basis of the data.
The present invention will now be explained in more detail with reference to embodiments and Figures.